1. Field of the Invention
The present invention relates to a disk drive and more particularly to a magnetic disk drive having a head stack assembly with a pass-through flex circuit cable.
2. Description of the Prior Art and Related Information
A typical hard disk drive includes a head disk assembly ("HDA") and a printed circuit board assembly ("PCBA"). The HDA includes at least one magnetic disk ("disk"), a spindle motor for rotating the disk, and a head stack assembly ("HSA") that includes a transducer head ("head") for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly ("HGA") that extends from the actuator assembly and biases the head towards the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
The industry presently prefers a "rotary" or "swing-type" actuator assembly which conventionally comprises an actuator body that rotates on a pivot assembly between limited positions, a coil portion that extends from one side of the actuator body to interact with one or more permanent magnets to form a voice coil motor, and an actuator arm that extends from an opposite side of the actuator body to support the HGA.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a head attached to the gimbal. The load beam has a spring function which provides a "gram load" biasing force and a hinge function which permits the head to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator am and a gimbal end that connects to the gimbal which carries the head and transmits the gram load biasing force to the head to "load" the head against the disk. A rapidly spinning disk develops a laminar air flow above its surface that lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be "flying" over the disk when in this state.
FIG. 1A shows a prior art HSA 820 having the above described portions, i.e. (1) an actuator assembly 830 comprising a coil portion 850, an actuator body 840, and an actuator arm 860; (2) an HGA 900 that includes a head 940; and (3) a flex cable assembly 980 including a flex circuit cable 950 and a flex clamp 959. The flex circuit cable 950 has a first portion 951 connected to a mounting surface 841 on a side of the actuator body and a dynamic loop portion 957 that permits relatively free rotation of the overall HSA. The first portion 951 generally carries a small number of electrical components (e.g. an integrated circuit 958 containing a pre-amplifier) and also contains a terminal pad portion 954 for connecting conductors within the flex cable circuit 950 to insulated wires (not shown) that lead to the head 940 and carry read and write signals transmitted to and from the head.
With reference to FIG. 1B, a substantially U-shaped flex cable guide 870 and a removable snap-fit pin 890 that fits inside the guide 870 and holds the flex circuit cable 950 against its inside surface are used in part to define a desired flex cable trajectory.
The head stack assembly 820 of FIGS. 1A-1B is usually assembled by combining the following subassemblies:
an actuator assembly 830; PA1 a plurality of HGA's 900 including pre-installed heads and wires; and PA1 a flex cable assembly 980 comprising the flex circuit cable 950, the flex clamp 959, and the electrical components (e.g. integrated circuit 958).
The three subassemblies are assembled into an overall head stack assembly by starting with the actuator assembly, staking or "swaging" the HGA's onto its arms, and then mounting the flex cable assembly to its mounting surface 841 (usually by making a solder connection 956 to a ground pin (not shown) and to a pair of coil pins 851). At this point, the partially completed head stack assembly appears substantially as shown in FIG. 1A. The head wires, however, must still be attached to the terminal pad portion 954 of the flex circuit cable 950.
However, the guide and pin structure shown in FIGS. 1A-1B may cause damage to the flex circuit cable when handling the head stack assembly during assembly and repair, takes up limited space that could accommodate additional electronic components, and crowds or restricts access to the terminal pad portion of the flex circuit cable.
As to potential damage, the U-guide 870 directs the flex cable circuit 950 forward once it is mounted to a side of the actuator body 840 as shown in FIG. 1A. As a result of this configuration, the flex circuit cable 950 must be pulled back around the outside surface of the U-guide 870 during assembly or handling and may be damaged. For example, the dynamic loop portion 957 limits access to terminal pad portion 954 when attaching the head wires to the terminal pad portion 954. Accordingly, the flex circuit cable 950 must be pulled back during this phase of assembly which may lead to damage of the flex circuit cable.
As to space concerns, the pin 890 limits the area available for mounting electronic components to the flex cable circuit 950 because such area must be kept clear for insertion of the pin 890. If the space next to the pin 890 is unavailable, then electronic components (e.g. integrated circuit 958) must be mounted closer to the terminal pad portion 954. This may encroach on the area needed to attach or repair the head wires in the terminal pad portion 954, particularly when using larger, ultrasonic bonding tools instead of thermal bonding tools. Ultrasonic bonding tools may be used when head wires of "MR heads" (i.e., heads which include magneto-resistive read transducers and inductive write transducers) are attached to terminal pad portion 954.